Mask and method to pattern chromeless phase lithography contact hole

ABSTRACT

A chromeless phase shift mask and Method for making and using. The A chromeless phase shift mask is used to pattern contact holes. The chromeless phase shift mask preferably comprises: a first phase shift region and a second phase shift region; the first region is comprised of a unit cell which is comprised of a rectangular center section and at least three rectangular sections (legs) outwards extending from the rectangular center section. The second region is adjacent to said first region. The interference between the first and second phase shift regions creates a contact hole pattern.

BACKGROUND OF INVENTION

1) Field of the Invention

This invention relates, in general, to masks used in makingsemiconductor devices and, more particularly, to making phase shiftmasks and using phase shift mask and more particularly to chromelessphase shift mask used to form contact hole patterns.

2) Description of the Prior Art

In the manufacturing of semiconductor devices small features or smallgeometric patterns are created by using conventional opticalphotolithography. Typically, optical photolithography is achieved byprojecting or by transmitting light through a pattern made of opticallyopaque areas and optically clear areas on a mask. The optically opaqueareas of the pattern block the light, thereby casting shadows andcreating dark areas, while the optically clear areas allow the light topass, thereby creating light areas. Once the light areas and dark areasare formed, they are projected onto and through a lens and subsequentlyonto a photosensitive layer on a semiconductor substrate. However, itshould be understood that dimensions can be scaled for use with otherreduction tools. Projecting light areas and dark areas on thephotosensitive layer results in portions of the photosensitive layerbeing exposed, while other portions of the photosensitive layer will beunexposed.

However, because of increased semiconductor device complexity, whichresults in increased pattern complexity, increased resolution demands,and increased pattern packing density on the mask, distance between anytwo opaque areas has decreased. By decreasing the distances between theopaque areas, small apertures are formed which diffract the light thatpasses through the apertures. The diffracted light results in effectsthat tend to spread or to bend the light as it passes so that the spacebetween the two opaque areas is not resolved, therefore makingdiffraction a severe limiting factor for conventional opticalphotolithography.

A method for dealing with diffraction effects in conventional opticalphotolithography is achieved by using a chromeless phase shift mask,which replaces the previously discussed mask. Generally, with lightbeing thought of as a wave, phase shifting with a chromeless phase shiftmask is achieved by effecting a change in timing or by effecting a shiftin waveform of a regular sinusoidal pattern of light waves thatpropagate through a transparent material. Typically, phase shifting isachieved by passing light through areas of a transparent material ofeither differing thicknesses or through materials with differentrefractive indexes, thereby changing the phase or the period pattern ofthe light wave.

Chromeless phase shift masks reduce diffraction effects by combiningboth phase shifted light and nonphase shifted light so that constructiveand destructive interference takes place. Generally, a summation ofconstructive and destructive interference of phase shift masks resultsin improved resolution and in improved depth of focus of a projectedimage of an optical system.

Relevant patents include the following:

U.S. Pat. No. 6,376,130—Stanton—Chromeless alternating reticle forproducing semiconductor device features—An alternating phase shiftreticle for a capacitor layout scheme for a memory device and a methodfor its fabrication is disclosed. The alternating phase shift mask hasregions of 0 and 180 degree phase shifts arranged in a way such that allsides of each region corresponding to a given phase shift value arebounded by areas corresponding to an opposite phase shift value.

U.S. Pat. No. 6,623,895—Chen, et al.—shows a Hybrid phase shift mask—Themethod includes the steps of forming at least one non-critical featureon the mask utilizing one of a low-transmission phase shift mask(pattern) and a non-phase shifting mask (pattern), and forming at leastone critical feature on the mask utilizing a high-transmission phaseshift mask (pattern).

U.S. Pat. No. 5,863,712 Von Bunau, et al.—Pattern forming method,projection exposure system, and semiconductor device fabrication method.

U.S. Pat. No. 5,786,115—Kawabata, et al.—Mask producing method.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide structure and a method offabrication a chromeless phase shift mask which is characterized asfollows.

An example embodiment is a phase shift mask comprised of: a maskcomprised of a first phase shift region and a second phase shift region;the first phase shift region and the second phase shift region are about180 degrees out of phase;

the first phase shift region is comprised of at least a unit cell; theunit cell is comprised of (a) a center section and (b) at least threerectangular sections extending outwards from the center section; thecenter section has a rectangular shape;

the second phase shift region is adjacent to the first region;

the unit cell has a shape that when light passes through the mask, thedestructive interference between the first phase shift region and asecond phase shift region creates a contact hole pattern.

An example embodiment is a chromeless phase shift mask comprised of: amask comprised of a first phase shift region and a second phase shiftregion; the first phase shift region and the second phase shift regionare about 180 degrees out of phase;

the first phase shift region is comprised of unit cells, each unit cellcomprised of (1) an center section and (2) four rectangular sectionsextending outwards from the center section; the center section has arectangular shape; the unit cells are connected by adjacent rectangularsections to form a plurality of rows and columns;

the second phase shift region is adjacent to the first region;

whereby when light passes through the mask, the destructive interferencebetween the first phase shift region and a second phase shift regioncreates a contact hole pattern.

An example embodiment is a method for projecting patterns onto asemiconductor substrate comprising: providing an illumination source;

-   -   providing a phase shift mask that has a first phase shift region        and a second phase shift region; the first phase shift region        and the second phase shift region are about 180 degree out of        phase;    -   the first region comprised of a unit cell; the unit cell        comprised of (a) a center section and (b) at least three        rectangular sections extending outwards from the center section;        the center section has a rectangular shape; the unit cell has a        shape that when light passes through the mask, the destructive        interference between the first phase shift region and a second        phase shift region creates a contact hole pattern;    -   projecting light from the illumination source thru the phase        shift mask onto a semiconductor substrate.

The above and below advantages and features are of representativeembodiments only, and are not exhaustive and/or exclusive. They arepresented only to assist in understanding the invention. It should beunderstood that they are not representative of all the inventionsdefined by the claims, to be considered limitations on the invention asdefined by the claims, or limitations on equivalents to the claims. Forinstance, some of these advantages may be mutually contradictory, inthat they cannot be simultaneously present in a single embodiment.Similarly, some advantages are applicable to one aspect of theinvention, and inapplicable to others. Furthermore, certain aspects ofthe claimed invention have not been discussed herein. However, noinference should be drawn regarding those discussed herein relative tothose not discussed herein other than for purposes of space and reducingrepetition. Thus, this summary of features and advantages should not beconsidered dispositive in determining equivalence. Additional featuresand advantages of the invention will become apparent in the followingdescription, from the drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of a mask according to the embodiments ofthe present invention and further details of a process of fabricatingsuch a mask and devices with the mask in accordance with the embodimentsof the present invention will be more clearly understood from thefollowing description taken in conjunction with the accompanyingdrawings in which like reference numerals designate similar orcorresponding elements, regions and portions and in which:

FIG. 1 shows a representation of an embodiment of the mask having afirst (e.g., 180 degree) phase shift region 104 (cross-junction feature)that has a cross shape.

FIG. 2A shows a top down view of a PSM of an embodiment of theinvention.

FIG. 2B shows a cross sectional view thru a first region 12 in FIG. 2A.

FIGS. 3A, 3B and 3C show top plan representations of embodiments of theunit cell with the different length and width rectangular sections.

FIG. 4 shows a simulation of the contact hole projection of increasinglengths of rectangular sections of an example embodiment of theinvention.

FIG. 4A shows top plan view of a dense array (rows and columns) contactpattern according to an example embodiment of the invention.

FIG. 4B is a top down view of the resulting contact hole pattern fromthe mask in FIG. 4A that is projected onto photoresist according toexample embodiment of the invention.

FIG. 4C shows a top down image view of a chromes less PSM with a Densearray contact similar to that shown in FIG. 4A.

FIGS. 5A and 5B show a top down views of an embodiment of a chromelessPSM with a dense (simulated) contact hole array 516.

FIG. 6 shows a graph of the Intensity across section (white line) inFIG. 5B according to example embodiment of the invention.

FIGS. 7A and 7B are top down views of a chromeless mask that show acolumn 715 of misaligned contact holes 716A according to exampleembodiment of the invention.

FIGS. 8A and 8B show top down views of a mask with first phase shiftregions comprised of unit cells in a random contact pattern with“regulator phase feature” 801 added to regulate the intensity accordingto example embodiment of the invention.

FIG. 9 pictorially illustrates an optical system 150 that uses achromeless phase shift mask of an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in detail with reference to theaccompanying drawings. The embodiments of the present invention providesa structure and a method of forming a chromeless mask pattern used todefine contact holes. Other embodiments provide a method of using themask.

FIG. 1 shows a representation of an embodiment of the mask having afirst (e.g., 180 degree) phase shift region 104 (cross-junction feature)that has a cross shape. The mask is preferably the chromeless type. Thequasar illumination fields 102 are superimposed over the mask areas forillustration purposes.

We illuminate the embodiment's chromeless mask with a cross-junctionfeature using quasar illumination, to form a (contact) hole feature inthe photoresist at the center of the cross-junction of two phase lines.This is because unlike other area, there are no neighboring phase edgesto create the destructive interference. This structure can be used inthe chromeless phase lithography to define contact holes.

FIG. 1 shows the quasar illumination 102, and the first (e.g., 180degree) phase shift region 104 of a phase shift mask (PSM). No edges ataxis K-K′ and axis L-L′ interference at a certain first dimension resultin a hole formation.

The “certain first dimension” can be determined by computer simulation.Illuminating parameters, such as wavelength, partial coherency,illuminating sector angle and type of off-axis illuminations, willaffect the required edges separation dimension for formation of thecontact hole. For example, with a 248 nm wavelength, numerical aperturesetting 0.80 quasar illumination, outer partial coherency factor of 0.55and inner partial coherency factor of 0.30 at 30 deg illuminatingsector, the required dimension for a hole formation is about and morethan (70×4) nm on mask as with used on a projection system magnificationof 4 times.

A. Example Embodiment of a Phase Shifting Mask

FIG. 2A shows a top down view of a PSM of an embodiment of theinvention. FIG. 2B shows a cross sectional view thru a first region 12in FIG. 2A.

The chromeless PSM mask (e.g., mask substrate) 10 preferably comprises afirst phase shift region 12 and a second phase shift region 14. Thefirst and second phase shift regions are preferably about 180 degreesout of phase. For example, the first region 12 of 180 degree phase shiftand a second region 14 has a 0 degree phase shift, or viscera.

The first phase shift region is preferably comprised of a unit cell. Asshown in FIG. 2A, the unit cell 13 (24 20 32 28 36) preferably has anorthogonal cross shape with a rectangular center section 20 (see dashedcenter rectangle) and preferably four (legs) rectangular sections 24 2832 36 preferably connected to and outwards extending from therectangular center (middle) section 20. In an option shown FIG. 3C, theunit cell can be comprised of 3 rectangular sections. Unit cells canalso be joined together as show in

The center section 20 can also be a rectangle or other shape and is notrestricted to a square. As the roundness of the (circular contact holelight) shape and displacement are affected by proximity structures,hence optical proximity correction process may change the originalsquare shape to rectangle depending on the effect of neighboringstructures. If the proximity lights that influence the resultantintensity at the center location are all equal, then the center section(20) is a square. In other embodiments, the center section could takethe shape of a rectangle to correct the influence from the proximatelights.

The second region 14 is adjacent to the first region 12.

The sidewall of the trench that where region 12 and region 14 transitshould be ideally or as close to 90 deg as possible. The depth of thetrench depends on the wavelength, such that it generate an optical pathdifference of 180 deg. The minimum width dimension that can bemanufactured to-date is about 200 nm, but not restricted to thatdimension with the technology advancement. As mentioned in previoussection answer, the dimension is limited by the illumination parameters.

FIG. 2B shows an example cross sectional view thru the horizontal leg 3220 24 of the first region 12 in FIG. 2A in the mask or substrate 10. Themask can be a conventional phase shift substrate comprised of, forexample, quartz, silica glass or borosilicate glass. The mask can havetrenches or raised areas to define the first and second phase shiftregions.

Contact hole 16 (to be imaged on the resist layer) is located assignedas a (180 degrees) phase shift layer 12. All the orthogonal rectangularsections (legs) 24 28 32 36 are extended such that the resultingintensity will produce a hole 16 in the center of the line (in theresist) as shown in FIG. 2A. For sub-wavelength size contact holeprojections, the dimension width of the line/legs should be less thanhalf the illuminating wavelength and low inner and outer sigma factorshould be used. Fine tuning can be achieve with the edge movement asshown in FIG. 4.

For illustration, a quasar 30 deg illumination angle, Wavelength=0.248um, NA=0.80, sigma inner of 0.30 and sigma outer of 0.55.

In general, for initial parameter assignment (before proximitycorrection), L₁ is approximately equal to W₁. D₁ should also preferablybe equal to W₁ for ease of designing the layout.

B. Embodiments of the Unit Cell with the Different Length and WidthRectangular Sections

FIGS. 3A and 3B show embodiments of the unit cell with the differentlength and width rectangular sections (legs). FIG. 3A shows the lengthL2 x L2 y of the rectangular sections and W2 widths of the rectangularsections. As the rectangular section length (L) increases, the diameterof the projected contact hole (D₂) increase. However, the relationshipis non-linear. The size of D_(x) will saturate at even thought L_(x)increases.

FIG. 3A shows a cross with the legs about twice as long as in FIG. 2A.

Using the above-mention illuminating parameters for illustration, L islength of rectangular section, W is width of rectangular section, D isdiameter of projected hole, the length of a side of the center sectionis also, W.

1. L₁=W₁=0.100 um, D₁=0.125 um.

2. L₂=0.150 um, W₂=0.100 um, D₂0.137 um.

3. L₃=0.200 um, W₃=0.100 um, D₃=0.144 um.

4. L₄=0.300 um, W₄=0.100 um, D₄=0.146 um.

5. L₅=0.050 um, W₅=0.100 um, D₅=0.00 um.

6. L₆=0.130 um, W₆=0.100 um, D₆=0.135 um.

FIG. 3B

As shown in FIG. 3B, if the legs L₃ get shorter than the leg's “criticaldimension” of 0.07 um when W is 0.100 um, hence no contact hole isformed for any smaller dimension. However, if L₃ is decreases, thegeneral trend is a decrease in D₃. From the illustration,

1. L₃=0.4 W₃=0.040 um, W₃=0.100 um, D₃=0.00 um.

2. L₄=0.7 W₄=0.070 um, W₄=0.100 um, D₄=0.034 um.

3. L₅=0.8 W₅=0.080 um, W₅=0.100 um, D₅=0.088 um.

C. Simulation of the Contact Hole Projection

FIG. 4 shows a simulation of the contact hole projection of increasinglengths of rectangular sections. FIG. 4 shows that as the legs getlonger, the hole gets bigger till it saturates at a dimension dependenton the illumination.

Referring to FIG. 4, the lines around the outside shows the computersimulated resist boundary at an intensity threshold of 0.30. The regionoutside the boundary indicates the resist is exposed and will be developand rinse away during the developing cycle.

D. Dense Array Contact Pattern

FIGS. 4A and 4B, show a dense array (rows and columns) contact pattern.FIG. 4A is a top down view of the mask and first phase shift region 412(e.g., 180 degree phase shift region) comprised of unit cells and secondphase shift region 414 (e.g., unshifted regions). FIG. 4B is a top downview of the resulting contact hole pattern that is projected ontophotoresist. If Wx is equal to Wy, then 2*Ly should be greater than Wx.2*Ly should then be approximately greater by at least 1.4 times of Wx.This is because at close proximity, such that 2*Ly is less than 1.4times of Wx, all the edges will interfere and no contact hole can beformed.

FIG. 4B shows the resulting contact hole pattern in the photo resist. Dis the diameter of the contact hole pattern 420.

FIG. 4C shows a top down image view of a chromes less PSM with a Densearray contact similar to that shown in FIG. 4A.

E. Example Embodiment of Chromes Less PSM

FIGS. 5A and 5B show a top down views of an embodiment of a chromelessPSM with a dense (simulated) contact hole array 516 can be patternedusing the unit cells 512 (e.g., 180 degree shift regions) with novelphase regulator features 501 added to regulate the intensity. Thenon-patterned regions 514 preferably have about 180 a phase shiftcompared to the unit cells 512 and phase regulator feature 501. FIG. 5Ashows at least two columns 512 comprised of unit cells; the two columnsare spaced apart; a regulator feature 501 between the two columns.

FIG. 5A is a schematic top down view. FIG. 5B is a photographic top downviews of an embodiment of a chromeless PSM with a dense array contactcan be pattern with novel phase regulator features 501 added to regulatethe intensity.

Phase regulator feature 501 is to create destructive interference at thebackground region where there is no contact hole feature present. Theedge of the (unit cell(s) 512) cross legs will interfere with thenearest edge of the phase feature 501. The width of the phase regulatorfeature is between 1 to 2 times the width of the cross feature (unitcell) used. It is placed with a spacing of at least 0.5 times the widthof the (unit cell) cross feature used and more preferably about 0.5 timethe width of the center section of the unit cell. Strips of phasefeature 501 can be used at spacing of the cross feature width for largebackground region. Else a chrome feature could be used to cover thebackground region.

FIG. 6 shows the Intensity across section (white line) in FIG. 5B. Usingthe illustrated illumination condition, sub-wavelength contact hole withdimension of about 0.107 μm can be patterned using 248 nm-wavelengthsource photolithography with this embodiment.

F. Example Chromeless Mask with a Column of Misaligned Contact Holes

FIG. 7A is an top down view of a chromeless mask that shows a column 715of misaligned contact holes 716A. FIG. 7A shows aligned contact holescolumns 717 of aligned (simulated) contact holes 716. FIG. 7B is animage of a chromeless mask that shows a misaligned contact hole. Innormal circuit layout, not all holes are neatly arranged in array. Insome instance, misalignment/skewing of a block of array of hole canoccur. This embodiment can also handle such cases using the same crossshape approach. FIGS. 7A and 7B show the embodiments “regulator phasefeatures” 701 and 702 added to achieve the correct contact hole pattern.

FIG. 7A shows at least two columns comprised of unit cells; the twocolumns are spaced apart and mis-aligned in an x or y direction; atleast a regulator feature between the two columns.

G. Contact Pattern With “Regulator Phase Feature”

FIG. 8A shows top down view of a mask with first phase shift regionscomprised of unit cells 801 in a random contact pattern with “regulatorphase feature” 801 added to regulate the intensity. FIG. 8B is a topdown image of a mask with first phase shift regions comprised of unitcells in a random (simulated) Contact hole 816 pattern with “regulatorphase feature” 801 added to regulate the intensity. The BLACK backgroundis 180 deg phase shifted quartz, all the Grey blocks are 0 deg phaseshifted quartz “phase features”. The WHITE features are the simulatedcontact hole opening. They appeared displaced from the contact locationand vary in sizes, as no proximity correction is done with thisillustration.

FIG. 8A shows the first region comprised of a double cell 822 comprisedof at least two unit cells are joined and at least a first separate unitcell 812. The double cell 822 and the first unit cell 812 are separatedby at least a regulator feature (814 or 801)

H. Method to Use the Mask to Expose a Wafer

FIG. 9 pictorially illustrates an optical system 150 that uses achromeless phase shift mask of an embodiment of the present invention.Generally, illumination source 155 is a lamp which emits commonly usedfrequencies, such as i-line (365 nanometers). However, other sources ofillumination can be used, such as excimer laser with wavelength of 248nm, 193 nm and 157 nm. Arrows 151 illustrate illumination that isdirected from illumination source 155 towards a chromeless phase shiftmask 152 which can be mask 10. The illumination, that is depicted byarrows 151, then passes through chromeless phase shift mask 152, wherethe illumination wave form changes. Arrows 153 illustrate the effectiveillumination after passing through chromeless phase shift mask 152.Illumination depicted by arrows 153 falls on a lens 154. Numericalaperture of lens 154, generally, ranges between values of 0.5 to 0.85.However, it should be understood that numerical aperture is a physicalattribute of the lens optics, and numerical aperture will improve orapproach a theoretical limit as lens optics improves, e.g., numericalaperture will approach 1.0. With immersion lithography the numericalaperture can be up to 1.44, depending on the refractive index of themedium. Typically, lens 154 is a reduction lens which reduces an imagethat is made by phase shift mask 152. This reduced image is projectedonto a surface of a semiconductor substrate 158. Arrows 157 representthe projection of the reduced image from lens 154 to semiconductorsubstrate 158.

I. Non-Limiting Embodiments

In the above description numerous specific details are set forth such asflow rates, pressure settings, thicknesses, etc., in order to provide amore thorough understanding of the present invention. It will beobvious, however, to one skilled in the art that the present inventionmay be practiced without these details. In other instances, well knownprocess have not been described in detail in order to not unnecessarilyobscure the present invention.

Although this invention has been described relative to specificinsulating materials, conductive materials and apparatuses fordepositing and etching these materials, it is not limited to thespecific materials or apparatuses but only to their specificcharacteristics, such as conformal and nonconformal, and capabilities,such as depositing and etching, and other materials and apparatus can besubstituted as is well understood by those skilled in themicroelectronics arts after appreciating the present invention

Unless explicitly stated otherwise, each numerical value and rangeshould be interpreted as being approximate as if the word about orapproximately preceded the value of the value or range.

Given the variety of embodiments of the present invention justdescribed, the above description and illustrations show not be taken aslimiting the scope of the present invention defined by the claims.

While the invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of the invention. It isintended to cover various modifications and similar arrangements andprocedures, and the scope of the appended claims therefore should beaccorded the broadest interpretation so as to encompass all suchmodifications and similar arrangements and procedures.

1. A method for projecting patterns onto a semiconductor substratecomprising: providing an illumination source; providing a phase shiftmask that has a first phase shift region and a second phase shiftregion, the first shift region is disposed on a first layer of the maskand the second phase shift region on a second layer of the mask, whereinthe first and second phase shift regions are out of phase, the firstphase shift region comprises a continuous unit cell, wherein the unitcell comprises a center section and extension sections, the extensionsections are contiguous to and extend outwards from the center section,the distinct extension sections having a same width as the centersection, the second phase shift region is adjacent to the unit cell inthe first phase shift region; and projecting light from the illuminationsource through the phase shift mask onto the semiconductor substrate,wherein destructive interference between the first and second phaseshift regions due to shape of the unit cell creates a desired exposurepattern on a photosensitive layer on the substrate corresponding toabout the center section.
 2. The method of claim 1 wherein the dimensionwidth of the rectangular sections are less than half the illuminatingwavelength and low inner and outer sigma factors are used.
 3. A methodfor projecting patterns onto a semiconductor substrate comprising:providing an illumination source; providing a phase shift mask that hasa first phase shift region and a second phase shift region, wherein thefirst phase shift region is disposed on a first layer of the mask andthe second phase shift region is disposed on a second layer, the firstand second phase shift regions are out of phase, the first phase shiftregion including a continuous unit cell comprising a center section anddistinct extension sections, the extension sections are contiguous toand extend outwards from the center section, the distinct extensionsections having a same width as the center section, the center sectionhaving a rectangular shape, wherein the unit cell has a shape that whenlight passes through the mask, destructive interference between thefirst phase shift region and the second phase shift region creates adesired exposure pattern corresponding to about the center section;providing a lens system that receives the desired exposure pattern thatis projected from the phase shift mask; reducing the desired exposurepattern in the lens system; and projecting the reduced desired exposurepattern onto a photosensitive layer on the semiconductor substrate. 4.The method of claim 3 wherein the illumination source is an off-axistype illumination source.
 5. The method of claim 3 wherein theillumination source is a quasar type illumination source.
 6. The methodof claim 3 wherein the photosensitive layer comprises photoresist. 7.The method of claim 3 wherein the photosensitive layer comprises aphotoresist layer and the reduced desired exposure pattern comprises acontact hole pattern.
 8. The method of claim 3 wherein saidphotosensitive layer comprises a photoresist layer and the reduceddesired exposure pattern comprises a row or a column of contact holepatterns.
 9. The method of claim 3 wherein: the first phase shift regionhas a 180 degree shift and the second phase shift region has a zerodegree shift; or the first phase shift region has a 0 degree shift andthe second phase shift region has a 180 degree shift.
 10. The method ofclaim 3 wherein the unit cell has an orthogonal cross shape with thedistinct extension sections extending outwards from the center section.11. The method of claim 3 wherein the unit cell has a T shape with threedistinct extension sections extending outwards from the center section.12. The method of claim 3 wherein the unit cell has an orthogonal crossshape with the center section having a square shape and four distinctsquare shaped rectangular sections extending outwards from the squarecenter section, the center section and the rectangular sections have thesame length sides.
 13. The method of claim 3 wherein the extensionsections have a minimum length between 70 and 200% of the width of thecenter section.
 14. The method of claim 3 wherein the first regioncomprises a plurality of unit cells arranged in a row or columnformation whereby contact holes are formed in row or column under thecenter sections.
 15. A method of forming a semiconductor devicecomprising: providing a substrate; and patterning the substratecomprising providing a mask with first and second phase shift regionswhich are out of phase, the first phase shift region comprising acontinuous unit cell, wherein the unit cell is disposed in the firstphase shift region and comprises a central portion and distinctextension portions which are contiguous to and extend from the centralportion, the distinct extension sections having a same width as thecentral portion, and exposing the substrate with an illumination sourceusing the mask, wherein destructive interference between the first andsecond phase shift regions due to shape of the unit cell produces adesired exposure pattern on the substrate.
 16. The method of claim 15wherein the central and distinct extension portions comprise rectangularshaped portions.
 17. The method of claim 16 wherein the unit cellcomprises at least three distinct extension portions extending from atleast three sides of the central portion.
 18. The method of claim 16wherein the unit cell comprises four distinct extension portionsextending from sides of the central portion.
 19. The method of claim 15wherein the unit cell comprises at least three distinct extensionportions extending from the central portion.
 20. The method of claim 15wherein the unit comprises four distinct extension portions extendingfrom the central portion.
 21. The method of claim 15 wherein the unitcell comprises three distinct extension portions extending from at leastthree sides of the central portion to form a T-shaped unit cell.
 22. Themethod of claim 15 wherein the unit cell comprises four distinctextension portions extending from the central portion to form across-shaped unit cell.
 23. The method of claim 15 wherein the desiredexposure pattern corresponds to a location at about the central portion.24. The method of claim 23 wherein the desired exposure patterncomprises a contact opening.
 25. The method of claim 15 wherein the maskcomprises a plurality of unit cells configured to form a plurality ofdesired exposure patterns.
 26. The method of claim 25 wherein thedesired exposure patterns comprise a plurality of contact openings. 27.The method of claim 25 wherein the desired exposure patterns correspondto a location at about the central portions of the unit cells.
 28. Themethod of claim 25 wherein the desired exposure patterns comprise aplurality of contact openings arranged in an array.
 29. The method ofclaim 28 wherein the desired exposure patterns correspond to a locationat about the central portions of the unit cells.
 30. The method of claim15 wherein the substrate is prepared with a photosensitive layer. 31.The method of claim 30 wherein the desired exposure pattern comprises acontact opening.
 32. The method of claim 30 wherein the mask comprises aplurality of unit cells configured to form a plurality of desiredexposure patterns.
 33. The method of claim 32 wherein the desiredexposure patterns comprise a plurality of contact openings.
 34. Themethod of claim 1 wherein length and width of the distinct extensionsections determine a size of the desired exposure pattern.
 35. Themethod of claim 3 wherein length and width of the distinct extensionsections determine a size of the desired exposure pattern.
 36. Themethod of claim 15 wherein length and width of the distinct extensionsections determine a size of the desired exposure pattern.